[YouTube] Add ability to download more playlist metadata: view count, description, upload date, and annotations. It could be called --write-playlist-description and --write-playlist-json

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Description of your issue, suggested solution and other information

I want to analyze statistics of Youtube playlists. I read the readme and found the options --write-description and --write-info-json to download descriptions and JSON metadata for individual videos. However, to the best of my knowledge there currently is no way to download that information from playlists. I ctrl+f'd playlist and metadata a lot and tried a bunch of commands, so I'm pretty sure about this.

The closest command to what I want is I found is youtube-dl --skip-download --flat-playlist --dump-single-json [playlist_id]

This dumps per-video id and title, and also dumps some of the playlist metadata I want, specifically the playlist title and playlist uploader (in the keys "uploader", "uploader_id", and "uploader_url").

What I would like is for --dump-single-json or a similar command, like --dump-playlist-json, to be able to dump more information on the playlist.

The most important playlist information to get is the view count, description, and upload or update date of the playlist.

Is there a command that can get these data, or can this feature be added?

Additionally, I've noticed on some playlists that there is a different view with an additional uploader and comment section per video. Most playlists do not use these fields, but it's good information when it is there, so I want it too.

For example, this playlist redirects the url to &disable_polymer=true, showing a view with uploader information. I have also noticed that some playlists, which don't default to this detailed view, may have per-video comments when the view is shown. It's pretty rare, but that information might be useful to get when doing an analysis (perhaps even because it's so rare).

This is an example of a playlist that uses per-video annotations. Note that the default view doesn't show the annotations! Regardless, I'd like to be able to download those too if possible.

So the main playlist data to get are the view count, the description, and the update date (is there a separate uploaded or created date too?). Video count would also be useful, although it's possible to derive from the JSON. And if possible I'd like to be able to get the per-video comments/annotations fields too.

I would like to get these playlist metadatas. Can you add --write-playlist-description and --write-playlist-metadata features to get them?

(playlist thumbnail would be good, too)